There exists the following type of technologies: Namely, a plurality of computers are connected to each other via a network. At this time, each of these computers executes one and the same task application, thereby constructing a high-reliability and high-availability system. In particular, in order to ensure the task's continuity at the time of a failure, the fault-tolerant computer (which, hereinafter, will be referred to as “FTC”) technology has been in widespread use. Here, the FTC technology is a synchronization scheme for operating a large number of computers in a manner of being synchronized with each other. Moreover, in the above-described FTC technology, the synchronization scheme for implementing the lockstep scheme at CPU's bus-clock level has been in widespread use (refer to PATENT LITERATURE 1). In recent years, however, in accompaniment with growing complexity of the CPU's configuration, attention has been focused on the synchronization scheme at software level (refer to PATENT LITERATURE 2).